In recent years, the global environmental problem and the problem of future depletion of petroleum resources ascribable to mass consumption of fossil fuel such as petroleum and coal have been controversial issues, and accordingly GTL (hydrocarbon liquid fuel) and DME (dimethyl ether) which are clean fuels produced from natural gas and the like have been drawing attention. Source gas for producing GTL and DME is called synthesis gas and contains carbon monoxide and hydrogen.
As a method of producing such synthesis gas, there have been conventionally known a steam reforming method (SMR) reforming natural gas or the like by steam, a partial oxidization method (PDX) using oxygen in the absence of a catalyst, an autothermal reforming method (ATR method) causing an oxidation reaction using an oxygen burner and a steam reforming reaction in the same reactor, and the like. The present applicant has developed a new synthesis gas production process adopting a catalytic partial oxidation method (CPO method) which uses a device with a simpler structure and in which problems of the generation of soot, carbon precipitation, and the like during the reaction are reduced, compared with the above conventional methods.
The CPO method is a method for generating synthesis gas by bringing oxygen-containing gas into contact with hydrocarbon gas, which is separated from natural gas or the like, in the presence of a catalyst to partially oxidize the hydrocarbon gas. In this CPO method, it is necessary to supply a catalyst layer with the hydrocarbon gas and the oxygen-containing gas which have been fully mixed in a mixing vessel and are not in a combustion state. However, mixed gas in a premixture state in which these gases have been fully mixed is within a combustion range, and even in the mixed gas in a diffusive mixture state where these gases are not fully mixed, areas within the combustion range dispersedly exist, and therefore, there is a risk that an abrupt combustion reaction may occur during or after the mixing of the gases, due to the supply of ignition energy originating from, for example, pipe friction, backfire from the catalyst layer, or the like. Under such circumstances, it has been an important issue to develop a safe gas mixing device capable of suppressing the progress of such combustion reaction even if the combustion reaction occurs.
A patent document 1 describes a gas combustion device for gas-fueled boiler in which a packing layer of ceramic balls is disposed at an outlet of a gas mixing chamber which mixes fuel gas and air to produce premixed gas. In this art, owing to the disposition of the packing layer, gas flow passages in which the premixed gas passes are narrowed, whereby the premixed gas is supplied into a combustion chamber at higher velocity than turbulent burning velocity of the premixed gas and thus the backfire from the combustion chamber toward the gas mixing chamber is prevented. Though describing the art for preventing the backfire at the outlet from the gas mixing chamber, the patent document 1 gives no description of a problem of a combustion reaction in the mixing chamber. Further, a patent document 2 describes a mixture accelerating means for mixing a hydrogen producing raw material such as kerosene with steam in order to produce hydrogen-containing reformed gas in the presence of a reforming catalyst, but does not mention at all a problem of the combustion of the mixed substances.
Patent Document 1
Japanese Patent Application Laid-open No. 2005-249240: paragraph 0021 to paragraph 0022
Patent Document 2
Japanese Patent Application Laid-open No. 2006-76850: paragraph 0027